A traveling wave tube and klystron or the like are electron tubes which oscillate or amplify a high-frequency signal (microwaves) by interacting an electron beam ejected from an electron gun with the high-frequency signal. A composition example of the traveling wave tube 1 is illustrated in FIG. 9. The traveling wave tube includes an electron gun 10, a spiral-shape helix electrode 20, a collector electrode 30 and an anode electrode 40. The electron gun 10 ejects an electron beam 50. The helix electrode 20 is a high-frequency circuit which interacts the electron beam 50 ejected from the electron gun 10 with the high-frequency signal (microwaves). The collector electrode 30 captures the electron beam 50 outputted through the helix electrode 20. The anode electrode 40 draws out electrons from the electron gun 10 and leads the electron beam 50 ejected from the electron gun 10 into space surrounded by the helix electrode 20. The electron gun 10 includes a cathode electrode 11 which ejects thermal electrons and a heater 12 which gives thermal energy for ejecting thermal electrons to the cathode electrode 11.
The electron beam 50 ejected from the electron gun 10 is accelerated by electric potential difference between the cathode electrode 11 and the helix electrode 20, and is introduced into space surrounded by the helix electrode 20. The electron beam 50 travels through the space surrounded by the helix electrode 20 interacting with the high-frequency signal inputted from one end of the helix electrode 20. The electron beam 50 which has passed through the space surrounded by the helix electrode 20 is captured in the collector electrode 30. At that time, the high-frequency signal amplified by the interaction with the electron beam 50 is outputted from other end of the helix electrode 20.
A power supply apparatus 60 includes a helix power supply 61, a collector power supply 62 and a heater power supply 63. The helix power supply 61 supplies helix voltage (Ehel) between the helix electrode and the cathode electrode 11. The helix voltage (Ehel) supplied on the cathode electrode 11 is a negative DC (direct-current) voltage based on the electric potential of the helix electrode 20 (HELIX). The collector power supply 62 supplies the collector voltage (Ecol) between the collector electrode and the cathode electrode 11. The collector voltage (Ecol) supplied on the collector electrode 30 is a positive DC voltage based on the electric potential of the cathode electrode 11 (H/K). The heater power supply 63 supplies the heater voltage (Eh) between the cathode electrode 11 (H/K) and the heater 12. The heater voltage (Eh) supplied on the heater 12 is a negative DC voltage based on the electric potential of the cathode electrode 11 (H/K). The helix electrode 20 is usually connected to a case of the traveling wave tube 1 and grounded in the power supply apparatus 60.
Further, although FIG. 9 shows an exemplary configuration of the traveling wave tube 1 equipped with only one collector electrode 30, the traveling wave tube may also have a configuration in which a plurality of collector electrodes are provided. In FIG. 9, although a configuration in which the anode electrode 40 is connected with the helix electrode 20 in the power supply apparatus 60 is shown, the traveling wave tube may also have a configuration in which an anode voltage (Ea) is supplied between the cathode electrode 11 (H/K) and the anode electrode 40, and the anode voltage (Ea) is a positive DC voltage based on the electric potential of the cathode electrode 11 (H/K).
The helix voltage (Ehel), the collector voltage (Ecol) and the heater voltage (Eh) are generated by using the power supply apparatus which includes an inverter, a transformer and a rectifier circuit. The inverter converts a DC voltage supplied from outside into an AC (alternating current) voltage and supplies the converted AC voltage on a primary winding of the transformer as an output. The transformer performs voltage conversion of the AC voltage inputted to the primary winding, and outputs the AC voltage converted into a desired voltage from a secondary winding. The rectifier circuit converts the AC voltage outputted from the secondary winding of the transformer into the DC voltage which has a desired voltage value. Therefore, the power supply apparatus is provided for outputting the DC voltage having a desired voltage value necessary for each of the helix voltage (Ehel), the collector voltage (Ecol) and the heater voltage (Eh).
As a method for measuring an electric current which flows to the cathode electrode 11, the collector electrode 30, the helix electrode 20 or heater 12 of such a traveling wave tube, usually a method as shown in FIG. 10 in which an ammeter 70 is inserted in series between the electrode (in FIG. 10, cathode electrode 11) and the power supply apparatus 60 is considered.
However, high voltage (several kV to several 10 kV) is applied on the cathode electrode, the collector electrode and the heater. Therefore, when measuring the electric current which flows to the cathode electrode, the collector electrode and the heater by using such an ammeter 70, it is necessary to conduct secure insulation to the ammeter 70 in order to perform measurement work safely. It is because high voltage is also applied on the ammeter 70.
Further, it is necessary to prepare and use a special measurement apparatus and a special equipment in order to perform measurement of the electric current flowing to each electrode or voltage applied on each electrode of the traveling wave tube. Therefore, it is difficult to measure such electric current and the voltage simply under operating condition of the traveling wave tube.
Japanese Patent No. 2711897 discloses technology about a power supply apparatus which measures an electric current which flows to the collector electrode of the traveling wave tube with providing a special transformer for electric current detection and measurement.
The power supply apparatus according to this technology has a configuration in which the special transformer is inserted in series between a secondary winding (output side) of the voltage conversion transformer and the rectifier circuit. A couple of primary windings of this special transformer are inserted in series at the output side (secondary winding) of the voltage conversion transformer, and the output side (secondary winding) of the voltage conversion transformer is connected with the rectifier circuit. The rectifier circuit outputs a DC voltage having a high voltage value to the cathode electrode and the collector electrode of the traveling wave tube. By such configuration, an electric current, which corresponds to the electric current flowing to the collector electrode of the traveling wave tube, flows to the primary windings of the special transformer, then, at the secondary winding of the special transformer, an electric current which is proportional to the electric current flowing to the primary windings of the special transformer can be measured.
Here, in this power supply apparatus, the cathode current is measured and outputted as the measured current value by applying the following approximation: it is supposed that the helix current and the anode current are negligible small compared with the collector current and the cathode current, and these values are ignored; and it assumes that the cathode current is equal to the collector current.